It's because we are pretty passionate people. Some are passionate about the hardware, some about the OS, some about both, and some (like me) about computers in general.
I signed up here because I wanted to share a solution to a problem that a lot of people have been asking a solution for on the net: why shared computers stop showing up in Finder's sidebar (Leopard). Since I did not find a solution, and had AppleCare, I called them. After I got the solution, I wanted to share it with others.
I'm a fairly new Mac user (2006), but have a programmer/technical support person for 10 years now. It's very addictive to be able to contribute and help others. My philosophy is: if my experience (good and bad) can help another user have a good experience, it's worth sharing it.
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Patrick
I signed up because I had heard good things about the site through other forums and I am in the market for a MBP. I found this site to be a great resource thanks to people like you doing just what you mentioned.